The present invention relates generally to an ink jet printer having a color head and a monochrome head, and more particularly to an ink jet printer that is switchable, during a single scanning operation, between a color printing mode by the color head and a monochrome printing mode by the monochrome head.
Up until now, a print head of an ink jet type includes a nozzle, a pressure chamber, an ink supply system, an ink tank and a piezoelectric element, and records characters or images on a recording medium, like paper, etc., allowing ink particles to be injected from the nozzle, after transmitting the displacement and pressure generated at the piezoelectric element to the pressure chamber.
FIG. 1 is a block diagram of the conventional ink jet printer. The ink jet printer comprises a control unit 200 and a head carrier 202. To the control unit 200, a CPU 206 to control the whole, a memory 208, an interface 210 to connect to a host 204, a controller 212, an image memory 214, a mechanical driver 216 to drive a mechanism 218, and a drive waveform generation unit 220 are installed. To the head carrier 202, a color head drive unit 222, a monochrome head drive unit 224, a color head 226, and a monochrome head 228 are mounted. The monochrome or color image data sent from the host computer 204 to the control unit 200 is processed by the CPU 206 and written into the image memory 214. Of these image data, the color image data is split into color components, Y, M and C, and written into the image memory 214. When printing documents, etc. in the monochrome mode, the controller 212 sequentially reads monochrome data (K) from the image memory 214, corresponding to the nozzle layout of the head, and supplies the data to the monochrome head drive unit 222. As drive waveform data is already written in a waveform memory located in the controller 212 as monochrome drive waveform data, and the drive waveform data is continuously outputted to the drive waveform generation unit 220, and supplied to the monochrome head drive unit 224, after being converted into analog drive waveform. The monochrome data from the controller 212 is used to select drive waveform at the monochrome head drive unit 224, and the selected drive waveform is supplied to the monochrome head 228, so that the printer records characters or images on a record medium like the paper, etc., as the piezoelectric element drives ink particles to be injected from the nozzle.
Also, when printing color images, like photos or graphics, the conventional ink jet printer supplies a group of drive waveforms consisting of a plurality of drive waveforms corresponding to the number of intensities from the drive waveform generation unit 220 to the color head drive unit, based on the color waveform data written in a waveform memory of the controller, and further supplies them to the color head 26, after selecting waveform of intensities corresponding to the individual color data of Y, M, and C, to print multi-intensity color image. On the other hand, when printing binary images, like monochrome characters or line-drawings, the conventional printer supplies a group of drive waveforms with improved degree of resolution to obtain sharp image, in short, it supplies drive waveforms having higher frequency than in the case of color images, so as to upgrade resolution.
However, in the ink jet printer, in which the monochrome printing and the color printing share the use of the conventional drive waveform generation unit 220, if the printer must print the document 230 as shown in FIG. 2, in which the color photo 232 is inserted in the monochrome text 234, the printer cannot print the monochrome text 234 and the color photo 232 simultaneously, by performing only a single head scanning. Therefore, the printer traditionally prints the monochrome text 234 while the monochrome head 28 is scanning once, as setting high resolution for monochrome scanning, and then, it prints the remaining color photo 234 with the color head 226, in the same scanning position, after shifting to multi-intensity color scanning. Because of this, if monochrome text and color photo is intermingled while the head is scanning one stroke, the printer must divide scanning into two modes, multi-intensity color scanning and high-resolution monochrome scanning modes, thereby resulting in a problem that the printing speed can be reduced by half.
According to the ink jet printer of the present invention there is provided an ink jet printer that can print by a single scanning operation, even if monochrome images and color images are intermingled, to speed up the printing speed.
The present invention is directed to an ink jet printer comprising a color head having a plurality of nozzles arranged on a head carrier, each of the plurality of nozzles injecting color ink particles by the drive of a piezoelectric element; and a monochrome head having a plurality of nozzles arranged the head carrier, each of the plurality of nozzles injecting monochrome ink particles by the drive of a piezoelectric element; wherein the ink jet printer comprises a control unit which, within a single scanning of the head carrier, switches the printing mode between a color printing mode by the color head and a monochrome printing mode by the monochrome head, to thereby provide a control of printing. As described above, the ink jet printer in accordance with the present invention will be able to make simultaneous printing with high speed, switching between color image and monochrome image within a single scanning of the head carrier.
The control unit of the ink jet printer includes a color drive waveform generation unit which simultaneously generates a group of color drive waveforms representative of at least two types of color dots; a monochrome drive waveform generation unit which simultaneously generates a group of monochrome drive waveforms representative of at least two types of monochrome dots; a color data output unit which outputs color data for a single scanning from a color image, in synchronism with a single scanning of the head carrier; a monochrome data output unit which outputs monochrome data for a single scanning from a monochrome image, in synchronism with a single scanning of the head carrier; a color head drive unit which selects one waveform from the group of color drive waveforms, based on the color data, the color head drive unit supplying the selected one waveform to the piezoelectric element of the color head for the drive thereof; and a monochrome head drive unit which selects one waveform from the group of monochrome drive waveforms, based on the monochrome data, the monochrome head drive unit supplying the selected one waveform to the piezoelectric element of the monochrome head for the drive thereof. By virtue of this configuration of the control unit, in cases where color data and monochrome data are intermingled in the printing data for a single scanning of the head carrier, the control unit can select the color head drive waveform in response to the color data during the single scanning, and select the monochrome waveform drive signal in response to the monochrome data, to thereby provide a switching between the color printing mode and the monochrome printing mode. The color printing mode of the control unit is a multivalued intensity mode, and the monochrome printing mode of the control unit is a high-resolution mode in which the resolution of the monochrome head is integer times the resolution of the color head. As described above, the printer can ensure high quality image printing, as well as high-speed printing, as a result of setting the color printing mode to multivalued intensity mode, and the monochrome printing mode to high-resolution mode, even if color image including a full-color picture, etc., and monochrome image including line-drawing, etc. are intermingled. In the multivalued intensity mode of the control unit, the amount of ink particles of the color head is variable for each nozzle. The high resolution mode of the control unit can employ any one form of the followings for example.
(1) the resolution in the horizontal scanning direction of the monochrome head is integer times the resolution of the color head;
(2) the ink injection cycle of the monochrome head is integer times the ink injection cycle of the color head;
(3) a multiple of the ink injection cycle of the monochrome head relative to the ink injection cycle of the color head is equal to a multiple of the resolution in the vertical scanning direction of the monochrome head relative to the resolution in the vertical scanning direction of the color head;
(4) the resolution in the vertical scanning direction of the monochrome head is integer times the resolution in the vertical scanning direction of the color head;
(5) the number of nozzle lines of the monochrome head is integer times the number of nozzles lines for each color of the color head; and
(6) a multiple of the number of nozzle lines of the monochrome head relative to the number of nozzle lines for each color of the color head is equal to a multiple of the resolution of the monochrome head relative to the resolution of the color head in the horizontal scanning direction.
A basic drive frequency of a group of color drive waveforms generated by the color drive waveform generation unit is equal to a basic drive frequency of a group of monochrome drive waveforms generated by the monochrome drive waveform generation unit. In this case, at least one intensity waveform of the group of the monochrome drive waveforms is a drive waveform that allows ink particles to be injected twice or more during a single injection cycle of the group of the color drive waveforms. The color data supplied to the color head drive unit, and the monochrome data supplied to the monochrome head drive unit are a set of pixel data containing a plurality of bits, and the bit data of color pixels contains information representing ink particle diameters by the color drive waveform, while the bit data of monochrome pixels contains information representing dot positions by the monochrome drive waveform. The color head drive unit and the monochrome head drive unit include for each piezoelectric element an analog multiplexer of multi-input/single output which inputs a plurality of drive waveforms and selects any one waveform or does not perform selection at all, depending on the pixel data bit. The color drive waveform generation unit generates at least two types of color drive waveforms for different ink particle diameters, and the monochrome drive waveform generation unit generates at least two types of monochrome drive waveforms that can drive injection once or a plurality of times within a single monochrome cycle. For instance, the color drive waveform generation unit generates color drive waveforms for different ink particle diameters, such as large, medium, and small diameters. The monochrome drive waveform generation unit generates monochrome drive waveforms for all dot patterns with different positions, such as front, rear, and both front and rear positions. Common head control signals, including clock, shift, etc., are supplied both to the color head drive unit and the monochrome head drive unit. The color head drive unit and the monochrome head drive unit are mounted on the head carrier. The color drive waveform generation unit and the monochrome drive waveform generation unit include a waveform memory storing the group of drive waveform data, and an AD conversion unit which converts the group of drive waveform data simultaneously read out of the waveform memory, into analog waveforms.